1. Field of the Invention
The present invention relates to a rotary body of hard material with a plastic supporter and a method of manufacturing therefor, which comprises a metal or ceramic product such as a sphere or column and a plastic supporter which supports the metal or ceramic product rotatably in locating around the product or which is rotatably supported by the metal or ceramic product in relation thereto. The metal or ceramic products are those such as bearings including ball bearings, roller bearings and the like, conveyers including ball conveyers, roller conveyers and the like, chains including ball-connection chains, roller-connection chains and the like, gears with shafts, rotary members with a shaft such as a pulley, casters including ball casters, roller casters and the like, and other bearings used for any kind of apparatus and machines.
2. Description of the Prior Art
In the present invention, a column body defines the column body including a shaft and those which have a spherical portion or a column portion having a large diameter portion at an intermediate portion thereof or at the end portions thereof. A rotary body of hard material defines means that includes not only those rotatable with respect to a supporter therefor, but also those such as a gear having a shaft or a shaft with a pulley which are not rotatable per se in the state of use but rotatable around the shaft thereof. In other words, the rotary body of hard material includes those which are rotatable relative to the plastic supporter which is located on the periphery of the rotary body of hard material.
This kind of rotary body of hard material with the supporter in the prior art is now described with reference to FIG. 1(c) showing an embodiment of the present invention. In order to prevent a sphere body 1 from falling down by surrounding the entire periphery of an intermediate portion of a supporter by leaving its upper and lower surface exposed, it had to take such a construction that the supporter comprises two members which are divided into upper and lower portions by a central line of the spherical body 1 and a semi-spherical opening or hole had to be formed with each of the two members so as to hold the spherical body 1 in the upper and lower directions and support same.
However, as described hereinafter in the embodiment of the present invention, a clearance 3 necessary for rotation of the spherical body 1 is sufficient to be micron size. When the clearance 3 becomes large, the spherical body 1 chatters and does not rotate smoothly. As a result, such a construction of the clearance 3 and the spherical body 1 cannot be used for a precision machine.
Further, in order to form such a micron clearance 3 between the spherical body 1 and the supporter 2, it is necessary to form an extremely precise opening or hole of a hemisphere with each of the supporters 2, which are divided into two pieces. Particularly, it is troublesome to fit and fix the upper and lower supporters 2 by holding the spherical body 1 without shifting their own positions. When precise fitting of the supporters 2 is not carried out in such a state that there is no shifting of the supporter 2 in any direction of 360.degree. of the hole, the spherical body 1 does not rotate smoothly and sometimes does not rotate completely.